[quoted text, click to view] "Jochen Kalmbach" <nospam-Jochen.Kalmbach@holzma.de> wrote in message
news:Xns961FB8C254827JochenKalmbachholzm@207.46.248.16...
>> QueryPerformanceCounter returns a LARGE_INTEGER, which the
>> documentation states is equivalent to a signed 64-bit integer. My
>> question is, can QueryPerformanceCounter return negative values, or is
>> its output restricted to positive values? TIA!
>
> QueryperformanceCounter internaly sometimes uses the RDTSC instruction.
> And
> this value is an unsigned 64-bit value. Therefor if you interpret this
> value as signed, it might become negative...
To be exact, QPC/QPF use different counters under different circumstances. On my system, the clock used for these functions is much slower than the CPU clock; I believe it's using some clock on the motherboard. If you think about the multi-CPU case, RDTSC stops making sense. -- Tim Robinson MVP, Windows SDK
Hi all,
QueryPerformanceCounter returns a LARGE_INTEGER, which the documentation
states is equivalent to a signed 64-bit integer. My question is, can
QueryPerformanceCounter return negative values, or is its output restricted
to positive values? TIA!
Hi Bob Altman, [quoted text, click to view] > QueryPerformanceCounter returns a LARGE_INTEGER, which the
> documentation states is equivalent to a signed 64-bit integer. My
> question is, can QueryPerformanceCounter return negative values, or is
> its output restricted to positive values? TIA!
QueryperformanceCounter internaly sometimes uses the RDTSC instruction. And this value is an unsigned 64-bit value. Therefor if you interpret this value as signed, it might become negative... BUT: On current processor speeds (3GHz) it will take about 95 years of a continuous running CPU to reach the "negative" value. -- Greetings Jochen My blog about Win32 and .NET
Hi Tim Robinson, [quoted text, click to view] >>> QueryPerformanceCounter returns a LARGE_INTEGER, which the
>>> documentation states is equivalent to a signed 64-bit integer. My
>>> question is, can QueryPerformanceCounter return negative values, or
>>> is its output restricted to positive values? TIA!
>>
>> QueryperformanceCounter internaly sometimes uses the RDTSC
>> instruction. And
>> this value is an unsigned 64-bit value. Therefor if you interpret
>> this value as signed, it might become negative...
>
>
> To be exact, QPC/QPF use different counters under different
> circumstances. On my system, the clock used for these functions is
> much slower than the CPU clock; I believe it's using some clock on the
> motherboard. If you think about the multi-CPU case, RDTSC stops making
> sense.
I just wanted to show that in the fastes possible implementation (RDTSC), it will take 95 years to become negative! -- Greetings Jochen My blog about Win32 and .NET
But the TSC can be user-set to any value, at any time. Not that you'd want to, but anyone (typically) could. -- 40th Floor - Software @ http://40th.com/ iPlay : the ultimate audio player for PPCs mp3,mp4,m4a,aac,ogg,flac,wav,play & record
[quoted text, click to view] "Jochen Kalmbach" <nospam-Jochen.Kalmbach@holzma.de> wrote in message
news:Xns96204D8537AD9JochenKalmbachholzm@127.0.0.1...
[...]
>> To be exact, QPC/QPF use different counters under different
>> circumstances. On my system, the clock used for these functions is
>> much slower than the CPU clock; I believe it's using some clock on the
>> motherboard. If you think about the multi-CPU case, RDTSC stops making
>> sense.
>
> I just wanted to show that in the fastes possible implementation (RDTSC),
> it will take 95 years to become negative!
A fair point :). /me goes and tests Jochen's theory -- Tim Robinson MVP, Windows SDK
Hi , [quoted text, click to view] > But the TSC can be user-set to any value, at
> any time. Not that you'd want to, but anyone
> (typically) could.
Not 100% true... <quote> When the WRMSR instruction is used to write to the time-stamp counter, only the low order 32-bits of the time-stamp counter can be written to, and the highorder 32 bits cleared to all 0s. </quote> -- Greetings Jochen My blog about Win32 and .NET
JK- [Mon, 21 Mar 2005 22:28:33 -0800]: [quoted text, click to view] >Not 100% true...
Right you are ... not the full 64 bits since the P6, apparently all 64 in the P5. Do you have a P5 to try? I've got some...on the wall. Smart move in any case. -- 40th Floor - Software @ http://40th.com/ iPlay : the ultimate audio player for PPCs mp3,mp4,m4a,aac,ogg,flac,wav,play & record
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